A photographic process utilizing a silver halide has heretofore been widely used due to its excellent photographic characteristics such as sensitivity, control of gradation, etc., as compared with other photographic processes such as an electrophotographic process or a diazo photographic process. In recent years, with respect to image formation process for light-sensitive materials using a silver halide, a technique capable of easily and quickly obtaining an image has been developed by changing the conventional wet development process using, such as, a developing solution, into a dry development process such as a process using heat.
A heat-developable light-sensitive material is known in the art. Such heat-developable light-sensitive materials and processes therefor are described in, for example, Shashin Kogaku no Kiso, Corona Co., Ltd., pages 553-555, Eizo Joho, April 1978, page 40, Nebletts Handbook of Photography and Reprography, 7th Ed., Van Nostrand Reinhold Company, pages 32-33, U.S. Pat. Nos. 3,152,904, 3,301,678, 3,392,020 and 3,457,075, British Pat. Nos. 1,131,108 and 1,167,777, and Research Disclosure, June 1978, pages 9-15 (RD-17029).
Various processes for obtaining color images by a dry process have been proposed.
With respect to processes for forming color images by the reaction of an oxidation product of a developing agent with a coupler, it has been proposed to use a p-phenylenediamine type reducing agent and a phenolic coupler or an active methylene coupler as described in U.S. Pat. No. 3,531,286, a p-aminophenol type reducing agent as described in U.S. Pat. No. 3,761,270, a sulfonamidophenol type reducing agent as described in Belgian Pat. No. 802,519 and Research Disclosure, pages 31 and 32 (September, 1975) and the combination of a sulfonamidophenol type reducing agent and a 4-equivalent coupler as described in U.S. Pat. No. 4,021,240.
These processes, however, are disadvantageous in that turbid color images are formed, because a reduced silver image and a color image are simultaneously formed on the exposed area after heat-development. In order to eliminate these disadvantages, there have been proposed a process which comprises removing a silver image by liquid processing and a process which comprises transferring only the dye to another layer, for example, a sheet having an image receiving layer. However, the latter process is not desirable because it is not easy to transfer only the dye by distinguishing from unreacted substances.
Another process which comprises introducing a nitrogen-containing heterocyclic group into a dye, forming a silver salt and releasing a dye by heat-development has been proposed in Research Disclosure, RD-16966, pages 54-58 (May, 1978). According to this process, clear images can not be obtained because it is difficult to control the release of dyes from non-exposed areas, and thus it is not a generally applicable process.
Further, processes for forming a positive-working color image by a silver dye bleach process utilizing heat, with useful dyes and methods for bleaching are disclosed in, for example, Research Disclosure, RD-14433, pages 30-32 (April, 1976), ibid., RD-15227, pages 14-15 (December 1976) and U.S. Pat. No. 4,235,957.
However, these processes require an additional step and an additional material for accelerating bleaching of dyes, for example, heating with a superposed sheet of an activating agent. Furthermore, these processes are disadvantageous in that the resulting color images are gradually reduced and bleached by the coexisting free silver, etc. during storage for a long period of time.
Moreover, a process for forming a color image utilizing a leuco dye has been proposed in, for example, U.S. Pat. Nos. 3,985,565 and 4,022,617. This process is, however, disadvantageous in that it is difficult to stably incorporate the leuco dye in the photographic material and coloration gradually occurs during storage.
In addition, all of the above-described conventional processes generally require the development for a long period of time and the resulting images have high fogging and low density.